Orthotropic elastic constants for polyimide film

The orthotropic constants of polyimide film have been characterized using t he theory of elasticity of an anisotropic material, Experimental techniques coupled with the mechanics of orthotropic materials are used to determine all 9 independent orthotropic elastic constants (3 tensile moduli, 3 sheer moduli, and 3 Poisson's ratios) and 3 coefficients of thermal expansion. Vi brational holographic interferometry is used to determine the orthotropic a xes of symmetry. For this polyimide film, the two principal axes coincided with the machine and transverse directions, it is also used to evaluate the 2 in-place Poisson's ratios by measuring residual stresses in 2-D and 1-D square membranes. Using other instruments such as a high pressure gas dilat ometry apparatus, a tensile tester, a pressure-volume-temperature apparatus , a thermomechanical analyzer, and a torsion pendulum, the 7 other orthotro pic constants and the 3 coefficients of thermal expansion are determined.